1. Field of the Invention
This invention relates generally to a power punch press and, more particularly, to a motor-driven sliding bolster plate employed in conjunction with a power punch press including a bolster plate positioning mechanism and an electrical operating and interlock circuit.
2. Description of the Prior Art
In power punch presses, a sliding bolster plate is employed to move the lower section of a stamping die away from a position under the press ram which carries the upper mating section of the stamping die. In operation, an operator places a workpiece on the lower section of the die and depresses the actuating switches at the front of the press. The bolster plate slides into the press to a working position with the lower die section aligned under the press ram. The ram is operated to shape the workpiece by closing the die members together. Thereafter, the press ram is raised to separate the die members and the bolster plate is moved outwardly away from the press ram to a loading position permitting the operator to remove the finished workpiece and insert a new workpiece easily without reaching under the press ram. The cycle is then repeated.
The sliding bolster plate permits the operator to load a workpiece into the press without placing his hands between the die members thereby lessening the probability of injury to the operator should the press be operated mistakenly. The sliding bolster plate complies with the "no hands in the die" requirement of the Federal Occupational Safety and Health Act.
Conventionally, hydraulic, often pneumatic, cylinder-piston driven systems are utilized to reciprocate the bolster plate. In order to avoid rapid stops and starts of the bolster plate which would dislodge a workpiece from its correct position on the die, the bolster plate must be driven slowly which, as a result, reduces the efficiency and output of the press.
Ferris et al. U.S. Pat. No. 3,446,106 is illustrative of a punch press having a sliding bolster plate. Therein, the bolster plate is reciprocated by a hydraulic motor. When the bolster plate is moved to a work position, the press ram is reciprocated. Thereafter, the bolster plate is returned to a load position. While the press shown in Ferris et al generally has some of the conventional structural features incorporated into the punch press of the present invention, it does have some obvious drawbacks and disadvantageous features. Two of these disadvantageous features are (1) a sliding bolster plate which cannot be driven quickly without jarring stops and starts and (2) a sliding bolster plate which is not locked into place before the press ram is operated. The former is undesirable because the output rate of the press must be reduced to ensure work product of high quality. The latter is clearly undesirable because severe injury can be inflicted to the operator if there is premature operation and because the relatively expensive die members can be damaged if they are misaligned when they are closed together.